Nuclear pore complexes (NPCs) control the transport of proteins and nucleic acids between the nucleus and cytoplasm of every eukaryotic cell. The number and composition of NPCs in a nucleus will influence how a cell grows and responds to environmental cues; dysregulation of nucleoporins and of NPC density has been observed in several cancers. Evidence suggests that the number of NPCs assembled in a cell is regulated, as different cell types have characteristic set points of NPC density that are maintained throughout the cell cycle, but the regulatory network has not yet been defined. NPC numbers may be regulated by limiting the availability of nucleoporin components, and may be linked to the cell cycle by signals from cyclin-dependent kinases (Cdks). A goal of this proposal is to determine whether Cdks and/or other cell cycle regulators control NPC assembly, and to identify the nucleoporins that are targeted by these regulators. The Nup107/160 complex is an integral building block of the NPC and a possible Cdk target. Of its nine components, only Nup96 is degraded during mitosis. Conversely, overexpression of Nup96 slows the cell cycle, suggesting a means for bidirectional regulation between NPCs and the cell cycle. Nup96 expression levels will be perturbed and NPC number and cell cycle progression will be assessed to test the hypothesis that Nup96 links the timing and extent of NPC assembly to the cycle of cell division. Finally, as the Nup107/160 complex, including Nup96, is a major regulator of mRNA export through the NPC, it is possible that mRNA export capacity of NPCs also fluctuates through the cell cycle. Nup96 overexpression appears to specifically limit the cytoplasmic accumulation of cyclin D and Cdk6 mRNAs, thus slowing the cell cycle. The effects of perturbing Nup96 levels on bulk and specific mRNA export will be determined using recently developed techniques for tracking mRNA in living cells. Overall, these studies will illuminate the mechanisms used to modify the number, composition, and functionality of NPCs during the cycle of cell division.